[DE-542] Adding support for shards retrieval

[apetenchea]

Main changes

• Adding shards() method to Collection, reflecting /_api/collection/{collection-name}/shards. It will be available only in a cluster setup.

Minor patches

• Adding docstring for computed_values
• Updating driver version in request header
• Fixing test_database_misc_methods. Getting and setting log levels for individual servers is available only in a cluster.

[codecov-commenter]

Codecov Report

Merging #274 (410164c) into main (744a6e9) will decrease coverage by 0.18%.
Report is 8 commits behind head on main.
The diff coverage is 64.70%.

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@@            Coverage Diff             @@
##             main     #274      +/-   ##
==========================================
- Coverage   99.01%   98.84%   -0.18%     
==========================================
  Files          26       26              
  Lines        3958     3970      +12     
==========================================
+ Hits         3919     3924       +5     
- Misses         39       46       +7     

Files Changed	Coverage Δ
arango/client.py	98.41% <ø> (ø)
arango/http.py	100.00% <ø> (ø)
arango/collection.py	97.84% <60.00%> (-0.67%)	⬇️
arango/exceptions.py	100.00% <100.00%> (ø)
arango/request.py	94.44% <100.00%> (ø)

... and 1 file with indirect coverage changes